This invention relates to a superconducting magnet and, more particularly, to a superconducting coil of a superconducting magnet and its mounting within a vacuum vessel.
FIG. 1 shows a sectional view of a prior art magnet. In FIG. 1, numeral 1 designates a coil which generates a magnetic field 2 when current flows through its winding. In general, a small magnet generates a relatively weak magnetic field and is often used without utilizing a magnetic shield to contain radiation within its environment since the weak magnetic field exerts little influence on the surroundings. FIG. 2 shows a sectional view of another conventional magnet. In FIG. 2, numeral 1 designates a coil by which magnetic fluxes are generated. Numeral 3 designates a magnetic shield which is made of a ferromagnetic substance.
In FIG. 2, since the coil 1 has a large geometry and produces an intense magnetic field 2a within its environment, a magnetic shield 3 made of a ferromagnetic substance is employed for the purpose of preventing influence of the magnetic field on the surroundings (for example, influence on a magnetic disc for a computer installed nearby).
As can be seen in FIG. 1, the magnetic fluxes 2 which extend along the inner periphery of the coil 1 also extend outside the outer periphery of the coil 1 and are represented as loops. Thus, even though the magnetic fluxes 2 generated by the coil 1 are weak, they extend outside the outer periphery of the coil 1 and spread widely. When an intense field is generated, the effect on a magnetic disc device or the like in the immediate surroundings is unavoidable.
Referring to the magnet of FIG. 2, the magnetic fluxes 2a interlinking with the coil are contained by the magnetic shield 3 made of a ferromagnetic substance of high permeability disposed outside the outer periphery of the coil 1. Thus, the magnetic fluxes which pass outside the magnetic shield 3 are weakened. Accordingly, even when equipment liable to be influenced by a magnetic field is installed near the magnet, it is not influenced thereby.
To provide electromagnetic insulation for a superconducting magnet stored in a vessel having vacuum heat insulation, heretofore a magnetic shield of the type described above was disposed around the outer periphery of the vessel. However, with this arrangement, the vessel and shield occupy greater space when the vessel and the geometry of the superconducting magnet enlarge, making the double vessel structure of the magnetic shield and the vacuum heat insulation vessel costly to make.